apt_updates: textfile metrics of pending apt updates for the node exporter collector

apt_updates/defaults/main.yml

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+# Directory the node exporter reads textfile metrics from (the Debian default).
+apt_updates_textfile_dir: /var/lib/prometheus/node-exporter

apt_updates/tasks/main.yml

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+# The metrics run after apt-daily (update) and apt-daily-upgrade (upgrade), so they show the state apt
+# just reached without a timer of their own. The "-" lets a failing metrics run leave apt's units green.
+- name: Create the textfile directory
+  ansible.builtin.file:
+    path: "{{ apt_updates_textfile_dir }}"
+    state: directory
+    mode: "0755"
+
+- name: Install the apt metrics script
+  ansible.builtin.template:
+    src: apt-updates-metrics.j2
+    dest: /usr/local/sbin/apt-updates-metrics
+    mode: "0755"
+
+- name: Create the apt timers' drop-in directories
+  ansible.builtin.file:
+    path: /etc/systemd/system/{{ item }}.service.d
+    state: directory
+    mode: "0755"
+  loop:
+    - apt-daily
+    - apt-daily-upgrade
+
+- name: Run the apt metrics after the apt timers' services
+  ansible.builtin.copy:
+    dest: /etc/systemd/system/{{ item }}.service.d/apt-updates-metrics.conf
+    mode: "0644"
+    content: |
+      [Service]
+      ExecStartPost=-/usr/local/sbin/apt-updates-metrics
+  loop:
+    - apt-daily
+    - apt-daily-upgrade
+  register: apt_updates_dropins
+
+- name: Reload systemd after the apt metrics drop-ins
+  ansible.builtin.systemd:
+    daemon_reload: true
+  when: apt_updates_dropins.changed
+  # Check mode does not write the drop-ins.
+  ignore_errors: "{{ ansible_check_mode }}"

apt_updates/templates/apt-updates-metrics.j2

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+#!/bin/bash
+# Pending upgrades, held packages, reboot flag and age of the package lists as node exporter textfile
+# metrics. apt-daily and apt-daily-upgrade run it after their update and upgrade (drop-ins).
+set -euo pipefail
+
+host={{ inventory_hostname }}
+textfile_dir={{ apt_updates_textfile_dir }}
+out=$textfile_dir/apt_updates.prom
+tmp=$(mktemp "$textfile_dir/.apt_updates.XXXXXX")
+trap 'rm -f "$tmp"' EXIT
+
+arch=$(dpkg --print-architecture)
+
+# The simulated upgrade lists "Inst <package> [<installed>] (<candidate> <origin> [<arch>])" per package.
+# An origin containing "security" counts as security, everything else as regular.
+pending=$(apt-get -s upgrade | awk -v host="$host" -v arch="$arch" '
+  /^Inst / {
+    line = $0
+    sub(/^[^(]*\(/, "", line)
+    sub(/\).*$/, "", line)
+    n = split(line, f, " ")
+    pkg_arch = f[n]
+    gsub(/\[|\]/, "", pkg_arch)
+    origin = (n >= 3) ? f[2] : ""
+    kind = (tolower(origin) ~ /security/) ? "security" : "regular"
+    count[kind, pkg_arch]++
+  }
+  END {
+    if (!(("security", arch) in count)) count["security", arch] = 0
+    if (!(("regular", arch) in count)) count["regular", arch] = 0
+    for (key in count) {
+      split(key, k, SUBSEP)
+      printf "apt_upgrades_pending{host=\"%s\",origin=\"%s\",arch=\"%s\"} %d\n", host, k[1], k[2], count[key]
+    }
+  }')
+
+held=$(apt-mark showhold | wc -l)
+
+reboot=0
+if [[ -e /run/reboot-required ]]; then
+  reboot=1
+fi
+
+# Debian writes update-stamp, Ubuntu update-success-stamp; both are touched by a successful update.
+stamp=/var/lib/apt/periodic/update-success-stamp
+if [[ ! -e $stamp ]]; then
+  stamp=/var/lib/apt/periodic/update-stamp
+fi
+cache=$(stat -c %Y "$stamp")
+
+{
+  echo '# TYPE apt_upgrades_pending gauge'
+  echo "$pending"
+  echo '# TYPE apt_upgrades_held gauge'
+  echo "apt_upgrades_held{host=\"$host\"} $held"
+  echo '# TYPE node_reboot_required gauge'
+  echo "node_reboot_required{host=\"$host\"} $reboot"
+  echo '# TYPE apt_package_cache_timestamp_seconds gauge'
+  echo "apt_package_cache_timestamp_seconds{host=\"$host\"} $cache"
+} > "$tmp"
+
+chmod 0644 "$tmp"
+mv -f "$tmp" "$out"